Among acceleration sensors manufactured based on MEMS technology, there have been manufactured some acceleration sensors detecting a change of electrostatic capacity. For instance, an acceleration sensor of this type has a capacitor at a position between a fixed electrode fixed to a substrate and a movable electrode installed on a weight which is made relatively movable with respect to the substrate so as to detect acceleration associated with a change of electrostatic capacity in the capacitor (for instance, Japanese Laid-Open Patent Publication No. 11-344507). The acceleration sensor disclosed in Japanese Laid-Open Patent Publication No. 11-344507 is provided as a uniaxial acceleration sensor configured such that x-axis directional both ends of a weight (mass body) are connected to a substrate via supports fixed to the substrate and elastic members (for instance, springs) so as to allow the weight to move in the x-axis direction. Each of the springs used in the above uniaxial acceleration sensor is configured such that, in plane view (xy in-plane view), a long side and a short side are provided alternately and continuously so that the long side and the short side make a right angle, i.e., each long side of the spring stretches in y direction, in the Publication, perpendicular to elastic movement direction of the spring.
Besides the above-mentioned uniaxial acceleration sensor for detecting acceleration working in a single direction, there have been some three-dimensional acceleration sensors for detecting three dimensional acceleration, i.e., in x, y and z directions (for instance, Published Japanese Translation of PCT International Patent Application No. 2005-534016, Japanese Laid-Open Patent Publication No. 06-258340, Japanese Laid-Open Patent Publication No. 05-340960, Japanese Patent No. 2773495, Japanese Laid-Open Patent Publication No. 07-245413, Japanese Patent No. 3327595, etc.). For instance, an acceleration sensor disclosed in Translation Publication No. 2005-534016, is configured such that a weight is connected to a substrate through four connection sets each consisting of a spring and an arm fixed to the substrate so as allow the weight to move three dimensionally, i.e., with respect to x, y and z directions. Typically, acceleration working three dimensionally is detected according to a change of electrostatic capacity that is caused by a change of distance between movable electrodes installed on the weight and fixed electrodes in respective axis directions. A spring used in the above typical three-dimensional acceleration sensor is configured such that a long side and a short side are provided alternately and continuously and length of the long side and that of the short side are made almost equal.